In a message dated 6/5/98 11:15:10 AM Pacific Daylight Time,
[log in to unmask] writes:

>
>  Can anyone direct me to a technical reference detailing the work done to
>  show that exposed copper on component lead ends do not pose a solderability
>  problem?
>
>  I've searched the Technet Archives but only found vague references to a
>  Battelle paper with no further details.
>
>  Thanks in advance for any responses.
>
>  Rob Schetty
>  LeaRonal Inc
>  Freeport NY  USA

Hi Rob,

     Don't you mean exposed copper on lead ends doesn't pose a RELIABILITY
problem? Because it definately poses a solderability problem. Many times when
the cut and form is done on QFP devices, the toe of the leads will have
exposed copper that solder has a difficult time wetting to...sometimes it
will, and sometimes it won't. But it's not a problem.

      I've read a few articles in SMT magazine before where there's been
stress testing performed on leads that had toe fillets and ones that didn't,
there was no appreciable difference in the strength or reliability of the
joint between the two. The article I remember was written by two engineers
from Micron.

      Also in J-STD-001B on page 18, paragraph 9.2.5.3 it states: Exposed
Basis Metal - Incomplete solder wetting at the tip of through-hole component
leads, and the edges and/or periphery of printed board lands and conductors is
acceptable. Exposed basis metal on component lead ends is permissible.

-Steve Gregory-

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